text:
Why does the Canard Rotor Wing use a Canard?
Why does the canard rotor wing (CRW) use a canard?  The CRW is a helicopter using engine exhaust to drive the rotor.  The exhaust can be used in the normal way to drive the aircraft once high enough speed has been reached.  Why can't the CRW use a tail instead?

Well, it has to use a canard because if it didn't then it wouldn't be a canard rotor wing, would it?

The Canard rotor/wing demonstrator, later called the X-50 Dragonfly was a Stop-Rotor Rotary Wing Aircraft made by Boeing and DARPA to demonstrate the principle that a helicopter's rotor could be stopped in flight and act as a fixed wing (like in movie The Sixth Day).

Image from boeing.com
The canard is used in case of Boeing X-50 Dragonfly in order to overcome the transient aerodynamic loads that occurred during conversion from rotary to fixed-wing flight. During transition from rotary mode to fixed wing mode, the rotor is being unloaded and the aircraft has to produce enough lift. The designers used both a canard and horizontal stabilizer to overcome this problem.
From Canard Rotor/Wing Aircraft:

During development, analysis and testing indicated that the X-wing design encountered high transient aerodynamic loads during the conversion from rotary to fixed-wing flight. The CRW design addresses this issue by generating positive lift on both the canard and horizontal tail during conversion. By deploying the flapped canard and the full-flying horizontal tail, enough lift can be produced to support the weight of the aircraft, and the main rotor can be completely unloaded throughout the conversion maneuver.

The aircraft never made a conversion flight and the program was canceled.


text:
Why did the Daimler-Benz DB 605 compression ratio vary between cylinder banks?
The Daimler-Benz DB 605 was an inverted V12. The compression ratio of the 2 banks varied slightly. Why did the designers do this?

Compression ratio: 1:7.3 right bank, 1:7.5 left bank (museomotori.unipa.it)

source: Stack Exchange

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text:
Help reading a FAA departure procedure chart
I was hoping to get a few answers regarding how to read a FAA departure procedure chart.  Let's take the JUDTH SEVEN DEPARTURE chart shown below:

From what I can tell, it seems that the diagram in the upper left indicates that those taking off from either runway 3 or runway 21 should make an appropriate turn to heading 335 degrees.  Is this correct?

Following the "thence...," it says to expect RADAR vectors to GBN VORTAC.  So does this mean ATC will guide the aircraft to the GBN VORTAC fix?

Can someone explain what MOHAK TRANSITION (JUDTH7.MOHAK) means?  Is this saying that the MOHAK fix represents a transition to en route airspace from terminal airspace?

How would one identify the departure fix in this chart and in general?  Is the departure fix MOHAK? JUDTH? GILA?  Additionally, what would be the departure procedure transition fix?

Thanks!

Yes, but (a) listen out for the 'Altitude cleared to' which will be given before departure since no 'top altitude' is published.
(b) Depending on traffic, you may also be given a different heading from the published HDG335 (= "or as assigned by ATC")
"Expect radar vectors to GBS" means ATC will, after identifying you, give you vectors, and at some point give you a "cleared direct to GBS", remember this is an RNAV departure.
The leg between JUDTH and MOHAK is the Transition and ends at MOHAK, where presumably you will join your Airway.
I can say that the departure ends at JUDTH after which you are on the MOHAK transition that ends at MOHAK. Being an RNAV departure you have to be able to fly direct to any of these points by name and  continue by following the ATC clearance. The controller will not use the term 'departure fix', it'll always be by name.

IF in doubt, get briefed by a regular, and you can always query ATC.

Thanks @skipper44 for this answer!

You have a good grasp on departures so far.
This particular SID advises the pilot departing Runway 3/21 to turn heading 335° and expect Radar Vectors to the GBN VORTAC. This is normal procedure considering the fact that so many airports in the same area share SIDs. Not all airports will have a co-located Navaid from which to start a SID. In this case, ATC would vector the aircraft back around the Phoenix airspace to GBN (Southwest) since the original 335° heading would be taking the aircraft away from GBN (due True North). Depending on traffic and ATC availability, ATC might vector you to the 249 Radial between GBN and JUDTH.
On other SIDs, there will be multiple fixes from which to leave the SID and transition to the en route portion of your flight. You, and/or ATC would file/assign for the fix most directly on your route of flight. In this case, there is only one, MOHAK.

Thanks @Dean F. for the information!

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text:
Why would a flight take a detour on clean weather?
I was in a flight recently (march 22nd) from SBCF to SBGR (Brazil). It's usually a 1h10m flight, but mine took roughly 20 minutes more. I saw the flight path in FlightAware and there's an unexpected (to me) detour mid-flight:

I looked for other instances of this scheduled flight and there are more extreme cases, such as this one:

In this case, the actual flight distance was 833km whereas the straight-line distance is measly 496km.
Obviously it would be difficult to pinpoint the exact reason why this happened, but what factors could lead to taking such a different than expected route?

The top picture appears to be a large S-turn, designed to slow down one airplane to increase spacing between it and the one in front of it.  Air Traffic Control needs airplanes to remain a certain minimum distance apart for safety.

In both examples, the aircraft was crossing the direct path between origin and destination, sometimes even flying perpendicular to the direct line. It would take more than one obstacle (like severe weather) to explain these patterns.
It is very likely that the pilots were deliberately delaying their arrival with respect to traffic congestion at the destination. See Why did this plane fly in a zigzag pattern?.

There are lots of reasons flights may not take a direct route, some are but not limited to:

It's just the route ATC assigned (for whatever reason they see fit)
There is an active military operations area or live firing area they are avoiding, these are not always "active" and may be avoided only sometimes.
Some kind of natural event on the ground, wildfire, volcanic eruption, etc.
There is a TFR they can't get through these are typically not hard bans on overflight but can be.
If it's an international flight they may not be allowed to overfly the airspace.
For smaller aircraft it may be a terrain avoidance issue (generally this is for general aviation sized planes).

Can it be for viewing nice spots? I was in a flight from Paris to Antananarivo back in June, and the pilots clearly took a detour to pass right next to Mount Kilimanjaro. They headed in straight line from Paris to Kilimanjaro, and then in straight line from Kilimanjaro to Antananarivo. It was so obvious by looking at the interactive map, I just couldn't imagine it was for another reason than having a nice view. The coincidence would have been too great IMO.

You say it was 'clear weather' but do you have anything to back that up other that what you saw outside the window? The pilots know what's ahead of them and it could be your smooth ride was down to their avoiding some heayy stuff. They could've seen some bad weather on their weather radar or maybe a pilot ahead alerted them.

Even if the weather actually is clear, there's always clear air turbulence if you want to make things interesting...


text:
Airplane gently rocking its wings during whole flight
I was on a flight with a regional airline a while ago in a Bombardier airplane (if I recall correctly) where the airplane would slowly and gently rock its wings just a little bit on the whole flight. I wasn't a long flight but wasn't very short either at roughly 2 hours.
It was very comfortable and the rocking made for a very gentle cradle feeling
My question is, why would that be? Is it economical to do so for any reason? Is it possible that the airplane had no autopilot and the pilot was flying it by hand? What could cause such a behaviour?

Sounds like the dutch roll mode was working. Were you high and fast at the time?

Are you talking about this? It is pretty common for airplanes.

I can give you two theories.  One is it's a very very mild case of "overcontrolling" of the autopilot roll servo as it chases a perfectly wings level condition and continuously applies a teeny bit too much left, ooops, then a teeny bit too much right, oops, and back and forth.
The aileron control circuit is cables running to hydraulics at the ailerons, with a spring loaded roller in a curvy V shaped cam device that centers each side of the aileron cable circuit. The breakout force to move the control circuit out of neutral (forcing the roller from the center V of the cam) is fairly high and this can actually be a problem for pilots hand flying at higher speeds where the ailerons are quite snappy - applying enough force to break out the circuit and move the wheel left gives too much, and back the other way... too much... and back and forth you go.  It can be a pain.
The autopilot servo is basically a little electric winch connected into the aileron cable circuit, doing the same thing the pilot does. It could be that something in the electronic control loop, or mechanically within the servo, can cause this back and forth oscillation on some airplanes, sometimes.  It may be related to wear and backlash within the autopilot servo.
The other theory is it's more or less something similar, but in the yaw mode with the yaw damper not able to fully dampen out a dutch roll mode because the amplitude was within the yaw damper's sensitivity band. Dutch roll is rolling due to yaw, which in swept wing jets is very strong, such that it can set up continuous self energizing oscillation.  It could also be related to wear and backlash in the yaw damper actuator, which is a pair of electric linear actuators (little electric screw jacks), in the push rods going to the rudder hydraulics.
If you saw the wing tip just going straight up and down, it's mostly likely the first theory.  If you could see the winglet moving in a little circle (indicating rolling and yawing), it's more likely the second theory.
I can really only theorize because the issue was never fully explored on the RJ program as this phenomenon was random, very minor and not dangerous, and was never complained about by operators because only someone sitting near the wings that can look straight out at the winglet ever notices it.  It was never bad enough to get anyone sick for example, at least on the RJ fleet.

For those who want to know the little tiny left, little tiny right would be a bad hysteresis. Similar to how you ac/heat does not come on right at the correct temp. It waits for it to be out of a range, higher for heat to turn off, lower for ac to turn off.

@NDEthos: Are they really using simple thermostat-style controllers instead of properly configured PID controllers?

I just used a thermostat as an example. Even with a PID I would assume the concept of hysteresis still applies.

But shouldn't an aircraft be roll-stable at cruise naturally?

It's way more complicated with swept wing airplanes because of the strong roll/yaw couple caused by the sweep.  The sweep is a bit like having way too much dihedral; any yawing motions set up sympathetic rolling motions (setting up a kind of S shaped flight path - dutch roll) and they may dampen themselves out, but in some configurations the damping is too weak, or is negative (dutch roll), necessitating a yaw damper system that works the rudder to actively stop or prevent yawing movements.  I suspect that the condition you were seeing was a feedback or hysterisis loop within the YD system.


text:
What exactly is the afterbody of an aircraft?
In my understanding the afterbody is everything trailing behind the nose of the craft excluding the wings and fuselage, and will thus include the empanage.
What exaclty is meant by the afterbody?

aftbody or afterbody?

Each vessel, whether land, sea, or air, should (might) have a defined afterbody. The afterbody is defined as:

The afterpart of a vehicle; The part of a vessel abaft midships; A companion body that trails a satellite or spacecraft; A section or piece of a launch vehicle, rocket, or spacecraft that enters the atmosphere unprotected behind the nose cone or other body that is protected for entry

and Merriam-Webster Online defines it as:

:  the after part of a body: such as
  a :  the part of a ship abaft midships
  b :  the bottom portion of a seaplane hull or float aft of the main step

To show you, visually, an easy to see set of examples, consider the following pictures of floatplanes (seaplanes):

In the first and second images, the afterbody is that part of the aircraft behind the step, which is the little 'notch' or, well, 'step' just behind the main wheels. In the third picture, the afterbody is everything after the step, which is the more steeply angled section under the wings. The step is generally just aft of the center of gravity of the plane.
Generally speaking, if one were to discuss the afterbody of a large airliners, such as the Airbus A380, the afterbody would be the fuselage from the wings back, but not including the tail (where the rudder and elevators are.) I could not find any Airbus references to 'afterbody' however. I did find some references to the afterbody of a Boeing 787, being that part of the plane behind the pressurized cabin, which is the very back of the plane, including the tail.
Not a very good solid definition where everyone agrees, sorry.

Well it does clear things up a little, thank you for the thorough answer.

On an airliner I would expect that the afterbody is the conical part aft of the cylindrical fuselage section. Whether that includes the tail surfaces is questionable. I would prefer to use other words.

I agree it is a very loosely defined term. The paper I am reading on fuselage design is constantly referring to 'afterbody' without ever defining it anywhere. The work was done by and for McDonnell Douglas so maybe they have a specific definition for it.

A very good answer I got from user Andries on Eng-Tips Forum:
"The afterbody is the rear section of the fuselage. The airflow in this region is often turbulent and afterbody design therefore has quite significant drag reduction issues . In many jet aircraft the afterbody contains the jet exhausts and their effect adds to the complexity of the design of this part of the fuselage."

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text:
How are aviation regulations treated on a global stage?
I know that the two large aviation regulatory authorities are the FAA and EASA, but every country also has its own civil aviation authority.
Focusing on airliners that need to operate all over the world, are they designed to meet FAA and EASA requirements only or are they subject to the regulations of every country in which they operate's regulatory authority?
Also, where does ICAO come into the picture?

Just to clarify, are you referring to airliners (i.e., the aeroplanes) or the airlines (i.e., the companies that operate the aircraft and carry passengers and cargo)?

Hi. I think there is surely plenty of overlap but I am mainly referring to the airliners, or airframers i.e. Boeing, Airbus etc.

EASA is not a regulatory authority. The European Union is.

I'm going to answer this from an aviation safety regulation viewpoint only. There are many broader considerations, such as criminal juristictions, employment, and environmental laws, which will have differing answers. I'll also add that my experience is with the Australian situation, but I don't think it varies too much around the world - happy to be corrected.
So with all that considered, the answer is... sort of both! The short answer is that they must follow the direct operating procedures of the country they are flying in, but some "back office" regulations do not apply.
Firstly to ICAO. This organisation isn't really concerned about individual airlines. Their primary purpose is to set international standards for the individual regulators to implement. But these Standards and Recommended Practices (SARPs) are not enforceable - individual states can simply lodge a 'difference' and continue to do their own thing. Another important job of ICAOs is to basically regulate the regulator, giving them a rating on how safe they are. The FAA and EASA also conduct their own audits for the same purpose.
Each airline needs to be certified in its home country with an Air Operators Certificate (or Part 121 Certification, or the many other variants around the world). Part of this process involves approving pretty much every single procedure the aircraft would ever do in normal operations - including the procedures at international ports. That means that for an Australian airline wanting to fly to LAX, the Australian regulator CASA has to inspect the port and approve it for use, checking that what the airline has proposed complies with the local airport procedures.
So, once the operations at LAX have been approved by CASA, the airline then approaches the FAA for a Foreign AOC/Part 121 approval etc (I'm not certain of the US naming convention). This certification process for a foreign certificate is almost always no way near as thorough as the full version. A lot of it depends on the home countries regulator and their status with ICAO or the FAA/EASA. If the FAA knows that the oversighting country is up to scratch, issuing the foreign certificate might just be a tick and flick exercise.
This 'foreign' status of this approval is key to your question, because many regulations are written like "the Part 121 operator must..." and NOT necessarily "the Foreign Part 121 operator must..."
Take a breath now and try to follow this. In the majority of occasions, the foreign approval says that the airline must operate in accordance with what has been approved by CASA. But, the procedures which CASA has approved are already tailored to LAX-specific operations! So you can see that the Australian airline has to obey the conditions of its FAA approval, which is to follow the operations set by CASA, which is to follow the US procedures!
But what if CASA and the FAA have differing regulations? We do have different requirements for things like fatigue management. Pilots who get a medical clearance here might not get one from the FAA. These 'risks' are pretty much just accepted by the regulators as being extremely unlikely to bring down a plane in their territory given the handful of flights a week they will be making. In extreme circumstances the FAA could place some sort of condition on the approval to further mitigate the risk of differing regulations.

Also, if the FAA a EASA or CASA etc. feel there's deficiency either in an airline or their regulators they will ban flights to/from their airspace until it's fixed. That gives each county an incentive to play nice and do their part.

I found it odd that the captain that landed the the 737 on a levee down in New Orleans was missing an eye. Obviously a top-notch pilot but no way would the FAA let him fly. The Salvadoran govt. was apparently not so sticky about that.

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text:
How do contrails form?
For my pre-scientific work I now need some general information about contrails. I searched for websites that explain the process of contrails being formed in detail but couldn't find any so far.
I realized this question hasn't been asked on Aviation.SE so far, so I decided to ask it now.
I would like to know, how the whole process works and what it needs for it to form a contrail.

What temperatures are needed?
How wet does the air have to be?
What exactly is a contrail then? Only condensation, ice, ..?
Is the contrail made from humidity from outside-air or from the vapor of the engine?
How does a contrail vanish again? What makes the difference between a 20 second contrail and a 2 hour contrail?
Everything that you know and is important to know.

Some of the questions may sound strange, but I found this topic is really complicated and also confusing and I want things to really understand now.
I (and probably many other people googling for this question in the future) would really appreciate a nice, informative, in detail answer, thanks!

Also: Do jet contrails impact weather?

I could have sworn this has been discussed on this site, before, but I can't seem to find it right now. I'm not sure why this has an off-topic vote, though. I don't see how this could possibly be off-topic.

Very much related: Why are contrails not visible from the cabin?

@reirab: Maybe it was in this question?

Contrails are formed from the condensation of jet exhaust.
When a hydrocarbon, such as jet fuel, is burned, it produces water vapor and carbon dioxide along with some impurities/unburned fuel. High altitude jets are in a much colder environment than ground temperature. Assuming a non-cloudy day, we can expect an approximate decrease of 5.4 degrees Fahrenheit for every 1,000 feet of elevation. Commercial jets fly around 28-35,000ft which translates to a roughly 150-160 degree decrease in the outside temperature. I'm not going to go into all of the physics behind it, but this is the most important point. It is much, much colder up in the air than down on the ground. And it is because of that coldness these contrails exist.
From here the lower temperature and outside pressure of the surrounding air create a ripe environment for condensation, as soon as a particle from one of the impurities in the fuel touch the vapor it condenses forming tiny water droplets and ice crystals. It's the same physical action that occurs when our breath produces a small 'fog' in the cold, and the same one that causes natural clouds to form in the first place.
You can also use contrails to tell the weather, high-humidity causes contrails to be thick and long-lasting which is a sign that a storm may be soon to come whereas a thin contrail or one that doesn't last long is a sign up low humidity.
To answer the rest of your questions:

What temperatures are needed?

That depends on a lot of factors, but in general they form when the air is colder than -34 degrees Fahrenheit.

How wet does the air have to be?

The air could be bone dry, the exhaust fumes themselves provide the water; though some of the latent humidity in the air is also heated and re-condensed adding to the effect.

What exactly is a contrail then? Only condensation, ice, ..?

A contrail is a mixture of condensation, ice, and trapped impurities from the exhaust.

Is the contrail made from humidity from outside-air or from the vapor of the engine?

The contrail is made from varying degrees of both.

How does a contrail vanish again? What makes the difference between a 20 second contrail and a 2 hour contrail?

A contrail is basically a cloud and vanishes the same way that clouds dissipate. Namely, temperature increase, mixing with drier air, or air sinking. All three will cause evaporation of the water droplets and dissipation of the cloud.
What makes the difference is primarily the external humidity. The more humid it is, the less a cloud or contrail can evaporate before reaching a state of equilibrium with the surrounding air

Everything that you know and is important to know.

The disturbance of the wingtips through humid air can kick off the same reaction, even near the ground. Though much less pronounced.

https://commons.wikimedia.org/wiki/File:C27_Spartan_making_condensation_spirals.jpg

The vortices in the picture are actually from the prop, and they are formed the same way as the ones from wingtips.

Correct JScarry, I should learn to triple-check before writing anything post 3am

@NoahWood. +1, but one comment/question. I am suspicious that engine contrails, unlike wing tip and prop tip condensation, is only from the water as a result of combustion, not in the intake (ambient) air. When the ambient air is ingested, and heated, then cools behind the aircraft, it can only decrease to the ambient temperature. So, if this causes it to condense, wouldn't it have been condensed when it was ingested, and so the aircraft was actually in a cloud? The static pressure of the exhaust will equalise with the atmosphere, and so not be a factor. Or have I missed something? Regards

Contrail from jet engines is primarily made up of water in the fuel, but some of the latent humidity will factor into it as well.
Temperature is directly correlated to pressure, as long as there's a temperature gradient there will be a pressure gradient as well and a jet engine can produce exhaust around 2,500Fahrenheit; plus just the general kinetic energy of the air you have as well.

And not every particle is doing the same thing in the atmosphere at the same time. Some will be evaporating as they soak up the heat from the condensation reaction; clouds and contrails will not form until condensation is happening quicker than the water molecules are torn apart by their own thermal energy.


text:
What is the spacing of obstacle lights on towers?
Radio antennas and other tall buildings have lights so pilots don't fly into them, especially at night. Is there a fixed spacing so you can determine the height of the tower by counting the lights?

In theory you might be able to make an estimate, but practically speaking it's impossible and a lot easier to just look at a sectional chart.
The FAA has a detailed guide on obstacle lighting standards, which usually applies to structures over 200ft in height but there's a lot of possible variation:

Recommendations on marking and/or lighting structures can vary
  depending on terrain features, weather patterns, geographic location,
  and in the case of wind turbines, number of structures and overall
  layout of design.

The actual number of lights and their placement depends on the type and size of the structure. Appendix 1 of the FAA guide has examples for water towers, radio masts, cooling stacks, bridges, chimneys etc. The vertical light spacing seems to vary from 250-375ft, depending on the structure type, but I didn't go through it systematically.
So if you have plenty of time you might be able to determine the approximate height of a structure by comparing its lighting layout to the guide and estimating based on that, but that's very unlikely to give you an accurate number. For a pilot in flight or planning a flight, that isn't safe or practical and the simple solution is to just look at the VFR sectional chart to get the height. For example, this tower is 1094ft high and the top is at 1994ft above sea level (so the ground level is 900ft above sea level at that location):

It wasn't clear from my question, but as a non-pilot, I was hoping to be able to determine the height of a mast by counting lights & multiplying. I guess I could at least get a rough estimate by assuming 250ft spacing?

@FreeMan You could do that but the margin of error would be very large. A completely different idea is to use a smartphone app.

Great tip! Hard to do, though, while driving, especially at night. I guess I'll just count and multiply, since precision isn't that critical from the car. It'll just be a good guideline. If I get really picky, I'll be sure to look it up later.

If you want to go look them up later, skyvector.com has sectional charts that you can zoom in and out of similarly to Google Maps.

There are regulations on the color, brightness, and location of lights, but counting them doesn't tell you how high it is.  You can tell the height by looking on a sectional, which lists the heights of obstacles next to the depiction.

Thanks, quite disappointing for a non-pilot wondering how tall that antenna really is.

ok, i didn't know you weren't a pilot, otherwise I would have given you @pondlife's answer :)

My inner 6-year-old still flies F-16s, does that count? ;)

@FreeMan You can easily obtain a reasonably accurate height measurement for any given tower by the stick method.


text:
What do the different colors of weather stations indicate on SkyVector?
In this particular map

from SkyVector, what are the meanings of the different colored circles, and for the different amounts of 'fill-in'?

It's obvious by hovering over them, that they are weather stations, as the weather info will pop-up, but there doesn't seem to be anything (to my untrained eye) about the weather pop up that would indicate a need for the different colors.
It's also obvious that the color doesn't indicate something permanent about the station, as last Friday, there were large swathes of different colors across the USA, while today almost everything is green.

Colors
At present1, they mean (image source):

For more details, please see this description.
Fill-ins
These are called sky/cloud coverage.

Image Source

1 From SkyVector:

The color is controversial because the FAA is making the NWS swap the
colors for VFR and MVFR. When the new aviationweather.gov becomes the
current aviationweather.gov, we'll change our colors to match.

Fantastic! Thank you. The SV link you posted wasn't particularly obvious from within SV...

You should add that the "fill in" is sky cover.

authors: Нямдорж Нямка


text:
What are the measurements for a "Black Box"?
I was wondering as to the measurements of  "black box" recorders. I have a new invention involving the "Black Box" and I need to know the measurements of the recorder.

you are wondering what, exactly? what quantities are measured? how often? why are recorded?

Please clarify what you are asking. Are you asking what the physical dimensions are? Are you asking what data they record? Something else? Do you have specific recorders in mind? FDR vs CVR?

google ARINC429 to learn about the data bus aircraft use, and then read up on the ARINC standards defining what goes over the bus, then just record everything you see.  Good luck!

The two main "black boxes" are the Flight Data Recorder (FDR) and the Cockpit Voice Recorder (CVR). These units are available from various manufacturers and therefore sizes vary. Many units can be used as either CVR or FDR, or as both.
A quick search provides a few examples:
etep Sentinel ED-112: CVR/FDR
Height: 3.929 in (9.980 cm)
Width: 4.970 in (12.624 cm)
Depth: 6.907 in (17.545 cm)
L3 F1000: FDR
Height: 7.62 in (19.4 cm)
Width: 4.88 in (12.4 cm)
Depth: 19.56 in (49.7 cm)
Universal Avionics Systems CVFDR: CVR/FDR
Height 6.1 in (15.5 cm)
Width 4.9 in (12.4 cm)
Depth 8.0 in (20.3 cm)
L3 SRVIVR: CVR/FDR
standard configuration:
Height: 3.25 in (8.26 cm)
Width 5.55 in (14.1 cm)
Depth: 6.55 in (16.6 cm)
extended configuration:
Height: 3.25 in (8.26 cm)
Width: 5.55 in (14.1 cm)
Depth: 7.2 in (18.3 cm)
L3 FA2100: CVR
Height 5.5 in. (14.00 cm)
Width 5.0 in. (12.70 cm)
Depth 12.6 in. (32.00 cm)
If you were asking something else, see:
How much data do FDR and CVR generate on commercial jets?
Or other questions already asked here.


text:
What is a 'deep stall' and how can pilots recover from it?
West Caribbean Airways Flight 708 which crashed in 2005, fell victim when their plane encountered a deep-stall. From my understanding, only certain planes can 'deep-stall'
How can pilots recover their plane to recover from a deep stall?

Are you asking only how to recover, or are you also asking about what a deep stall is? (I ask this because of the title of the question)

I'm asking both but more importantly about how the recovery is performed

A deep stall or a super stall is a condition where the wake of the wing impinges on the tail surface and renders it almost ineffective. The wing is fully stalled, so the airflow on its upper surface separates right after the leading edge, which produces a wide wake of decelerated, turbulent air. Consequently, the dynamic pressure at the tail surface is much smaller than in unstalled flight, which is the main reason for the reduced effectiveness.
Consider this case: The aircraft flies in a nose-up attitude, but on a downward flight path. Consequently, the angle of attack of the wing $\alpha$ is much beyond its normal operating range, causing a fully separated upper surface flow. Due to the T-tail configuration, the wake is hitting the elevator such that all of it is shielded from the regular airflow.

The pitching moment of this configuration over angle of attack (blue line) looks something like this. First there is a stable region with a negative gradient at low values of $\alpha$, followed by a minimum when the wing stalls, and then a region with a positive gradient, where the separation unfolds and the tail moves into the wake from above. This region is unstable in pitch, so without control input the aircraft will not stay there, but either pitch down or up until it reaches a stable region again. At high angles of attack follows another stable region with a negative gradient:

Note that we have two trim points, one in the regular range of the angle of attack, and one way out to the right. In both cases the aircraft has a stable trim condition, so small disturbances are answered with force changes which will keep the aircraft at one of these points. Between the two, there is another equilibrium point, but here the airplane is unstable. If it pitches up slightly there, the pitch up will accelerate until it reaches the upper trim point.
Now consider the control power of the horizontal tail. When it flies in undisturbed air, it can trim a wide range of angles of attack. In the deep stall condition, however, its control power is much reduced, resulting in a much smaller range of trimmable angles of attack. If the lower end of this range is right of the point where the pitching moment crosses into positive values (here at $\alpha$ = 24°), the aircraft cannot escape with elevator deflections!

Please note that the control power is not sufficient to enter the deep stall with quasi-stationary trim changes. The pilot needs to pitch up quickly and has to overshoot the static trim range in order to cross into the stable region above 30° angle of attack. There, his range of trimmable $\alpha$s is too small to achieve the same overshoot backwards.
To get out of this trap needs other changes: Either shift the center of gravity forward, or try to drop one wing. Unfortunately, both the ailerons and the rudder will also be much less effective due to the massive separation and the wake. In a number of cases, even experienced test pilots could not escape this condition.

Would asymmetric thrust in multi-engine aircraft be a useful technique to counter the degraded control surfaces?

@Hugh: Possibly, but I would expect that tail-mounted engines would not produce enough yawing moment. Wing-mounted engines, however, should. In the end, it depends on the details of the configuration.

@PeterKämpf I agree with your guess regarding tail vs. wing-mounted engines. The problem is that most aircraft that can enter a deep stall in the first place (T-tail configurations) have tail-mounted engines.

@reirab: Yes, the T-tail had been chosen in most cases to make place for the engines. And the engine mass means that the wing is closer to the tail, so the wake hits it at a higher angle of attack. I know that the C-141 had flutter problems during development (high mass of the horizontal on a long lever arm, mounted on a torsionally weakened fuselage due to the cargo ramp), but neither it nor the A400M had deep stall problems due to their swept wings. The T-tail of the A400M had been selected to reduce the height of the vertical by 2m, so existing hangars could be used.

"Either shift the center of gravity forward, or try to drop one wing. Unfortunately, both the ailerons and the rudder will also be much less effective due to the massive separation and the wake."  On the other hand, most airplanes tend to roll off all by themselves in a stall.  On the other other hand, rolling off and dropping a wing could send the plane into an uncontrolled spin, which apparently (at least for some aircraft) is or was considered even worse than a deep stall; (1/2)

(2/2) reading this account of an accidental deep stall in a prototype 727, the pilot in that case had to fight hard to keep it from rolling off into a spin (the test pilot was eventually able to power out of the deep stall using engine power).

@Vikki In a deep stall the rolling motion is strongly damped; rolling in a stall only happens at lower AoAs in the range where the wing's lift curve slope is negative. Now I have to wonder what is so much worse in a spin: In a deep stall the airplane is really uncontrollable while in a spin at least some part of the wing has attached flow and control inputs do have some effect. An "uncontrolled spin" can only be a flat spin, regular spins are easily controlled.

@PeterKämpf: Maybe the prototype 727 was (or was thought to be) susceptible to entering a flat spin from a stall?  Rereading the account of that incident, it looks like the FAA test pilot who precipitated the incident may have somehow managed to pitch the plane so far up that it reached an AoA of about 70°, which would place it in another negative-lift-curve-slope region and explain the strong rolling experienced, but also make the eventual recovery all the more remarkable.

A deep stall is a stall where the pilot is unable to pitch down due to either loss of clean airflow over the elevator (typical in T-tails) or the canards still producing lift while the wing behind it is stalled.
Depending on the aircraft the pilot may be able to bank and use the rudder to get the nose down to correct the stall. If possible the pilot may be able to move/ditch cargo to move the Center of Mass forward.

Cycling the landing gear is also a suggested technique if you are in a deep stall as the drag below the center of thrust may pull the nose down enough to break the stall.

@Articuno: Under "tail stall" I'd understand condition where the tail itself is stalled and therefore ineffective rather than being ineffective due to disturbed airflow behind the (stalled) wings. It is slightly different, but similarly difficult to recover.

@Articuno: I'd say it is not really well defined. The flow is already turbulent and won't attach to it at any angle of attack.

The cargo shifting perspective is very interesting. I guess this could be done by quickly moving fuel. Is there an aircraft that does this?

@AlbinStigo some airliners have trim tanks in the tail, but I don't think the pumps are fast enough to recover from stall that way.

It's assumed that deep stall mainly affects T tails, but high angles of attack may lead to a more conventional low tail design having the tail stalled.  If you look for the accident investigation animation of AF447 (youtube), you will see that there was a lot of ineffective stick movement.  Finally, when the stick went forward, the nose lowered to about 10 degrees down, but the flight path angle was close to -45 degrees, so the angle of attack was roughly 35 degrees.  Both surfaces were deeply stalled and this manoeuvre was survivable with conventional stall recovery.
There are recovery techniques which may work.  I used to air test a large T tail design and the briefed manoeuvre was to roll to induce side-slip which would reduce the angle of attack.  On a T tail design, this would mainly be accomplished by rudder.  But a low tail design may have the rudder blanked by the tail at these angles of attack.  The only way to induce roll from yaw in this case would be the use of asymmetric thrust.
The AF447 pilots were not equipped with this knowledge which may have saved the aircraft.  I have asked my colleagues their opinion and I get the impression there is not much appreciation of this situation.  With the recent Air Asia accident investigation follow a similar approach to the events leading to the loss of AF447, perhaps now is the time.

Welcome to Aviation.SE Simon!

In the AF447 crash the stick never went fully forward for more than a few seconds, I think that's too short to draw any conclusions from; before the airspeed increased they pulled back again hampering any change of stall recovery.

Watching that animation is soo frustrating. "push the stick forward.. PLEEAASSE!"

About AF447, there was no deep stall, but a "classical" stall. By pushing the stick a sufficient time, the crew would have recovered easily. Unfortunately, they did not maintained it forward. All traces and tests performed later on are very clear on this issue.

That animation is gut wrenching.

Why wouldn't they push forward? How many hours did the pilots have? 10?

@Cloud Suggest you go to the BEA website and download the report.  It is worth the read.

The article on stall in Wikipedia talks of one instance where a B727 recovered from a deep stall by "rocking the plane to higher bank angles" till the nose dropped and normal control response was recovered.

Deep stalls appears not only for the T tails aircraft. The CG far back will certainly be a good reason to have one of this type of stall. Nowadays the fighter jets are prone to get into the deep stall state. Recovery is done by pushing the nose down and power up.

"Recovery is done by pushing the nose down ..." Isn't the whole point of a deep stall that this no longer works?


text:
What happens when more than one agency investigates a plane crash?
Does one accident report overrule the other or would there be two possible outcomes for the disaster?
Some examples
EgyptAir Flight 990 had the NTSB and the ECAA investigate and produced two different reports.
SilkAir Flight 185 had the NTSB and the NTSC investigate and also produced two different reports.

@Articuno As in what is the process if two agencies investigate, thus producing 2 different reports. What if one report rules pilot error and another says mechanical error, is there ever a final verdict? Say it was pilot error vs mechanical error, would there be changes made to improve pilot training or would they fix the mechanical problem on all aircraft instead? This is what I'm trying to find out.

Two reports are published and everybody is free to believe whichever they choose.
According to ICAO rules the (investigation board1 of) country of occurrence (or country of operator if it happens over international waters) leads the investigation and (investigation boards of) country of operator, country of aircraft registration and country of aircraft manufacture are asked to take part in the investigation2. So it is expected that the investigators from country where the accident happened will publish the official report.
But some investigators may choose to publish their own report if agreement about the probable cause is not reached. Since even the official report does not have any legal effect (the investigation boards don't have any legal power), so it does not really matter much.
An accident report identifies factors that contributed to the accident and suggests improvements to safety practices to reduce risk of the accident reoccurring. But whether the recommendations are implemented depends on aviation authorities3, which are separate governmental bodies with legislative power. And they decide which recommendations they will incorporate into the legal rules.
Of course each such authority only has power over that country. So while the accident is investigated just once (even when multiple reports are published, the investigation is joint effort, just the investigators don't agree on the conclusion), the rules may be implemented differently in different countries. ICAO tries to coordinate, but it does not have any legal powers itself either. So it is up to the aviation authorities to choose which report they believe more.
Assigning blame is explicitly not purpose of the investigation according to ICAO rules. A criminal trial or civil litigation may be started about the accident by complaint from police, state attorney or damaged person, in which case the investigation report will likely appear as expertise in the court, but if there is not agreement between the investigators, it is again up to the court to decide which explanation it believes most.
Finally, the investigators not agreeing is rare in practice. Usually the investigation continues until they get something they can agree on; for several years if needed. Suspected intentional crashes by pilot (which is both cases you mention) seem to be the main exception as there may be political reasons why the leading investigators (from the same country the pilots were) don't want to accept that resolution.

1Investigation board in USA is NTSB, in Canada TSB (the most rigorous investigation board in the world (or at least they very carefully collect and report even the smallest incidents, see here)), in UK AAIB, in France BEA etc.
2It is not strictly necessary, but it is the usual setup. The country of occurrence handles most investigation on site, country of registration takes care of interviewing operator and maintenance personnel and country of manufacture cooperates with manufacturer on identifying mechanical damage and usually reads the FDR and CVR data as there are only a few labs in the world that do that. Plus some of the large investigation boards may be asked for additional help. And in politically sensitive cases like MH17 additional countries may be involved to reduce risk of manipulation with the results.
3Aviation authority in USA is FAA. In Europe there is EASA, which coordinates the regulations, and separate authorities in each country that carry out the actual oversight.

"in Canada TSB (the most rigorous investigation board in the world)", showing your National pride, or can this be backed up?

@CGCampbell: It is mentioned as reporting more incidents than others in http://avherald.com/h?article=45483425. Unfortunately there are no anchors, so I can't provide link to the particular question/answer. And for the record, I am not Canadian (and neither is the guy interviewed in that article).

@JanHudec Quantity doesn't always equate to quality - there's a joke about the paranoid pilot who files an ASRS report after every flight that gets told every so often. (Though the CTSB reports I've read tend to be generally excellent - I'm not sure about "most rigorous" but they're definitely in the top 3 for thoroughness!)

Does the FAA ever investigate flight crashes. Like in the movie Flight, it says "FAA took 10 pilots, placed them in simulators, recreated the events that led to this plane falling out of the sky. Every pilot crashed the aircraft, killed everybody on board. You were the only one who could do it!"

@Firee: No. It is NTSB who does that. FAA defines rules and checks they are followed.


text:
What is the range of an air traffic control tower's radio transmission?
What is the maximum distance the voice messages sent by the tower on a radio channel can be received by an aircraft?

VHF transmissions are limited by line of sight. So, assuming the transmitter is at the tower location, and assuming the aircraft is at cruise altitude (say F300, or 30,000 feet or more), the maximum range is perhaps 200 to 300 km before the curvature of the earth eliminates the line of sight. This also depends on weather conditions and the transmitter power.
In practice, VHF coverage may be extended using additional transceiver sites on the same (or different) frequency. This is particularly important in mountainous terrain.
For oceanic flights where there is no place to put additional transceiver sites, HF (shortwave) radio can be used which has a much greater range (thousands of km), especially at night. Some aircraft are also equipped with satellite phones so controllers can simply call them. However, this wouldn't be the tower controllers talking to the pilots over the ocean, as tower controllers aren't responsible for en route control.

Depends on how the antenna, radios, terrain, etc are configured.  I have experience some places that you needed to be very close < 10 miles.  And some places where you could hear ATIS at 60 miles.


text:
Crimes committed on board
I know a similar question was asked here before, but there is a difference:
Let's say person X is on a flight from Pakistan to Canada on PIA (national carrier of Pakistan). The aircraft lands at, say, Toronto Pearson Airport.
From what I gather after reading the Tokyo Convention, the aircraft is no longer in flight once the airplane doors have been opened for disembarkation.
If an offence occurred on the airplane once the doors have been opened for disembarkation, which country is responsible for prosecution? The country where the aircraft is registered or the country where the plane has landed?

When the door is open it's easy: the country where the aircraft is physically located. It's the case when door is closed that is difficult.

Once the doors have been opened, it's a pretty clear case: the crime happens on some sovereign soil, and that country is responsible. They are also most likely to get custody of the criminal, which as described in the other answer is a large part of who prosecutes.

i do have one more query though: Say person X, after having committed the offence on the plane (regardless of whether the airplane doors were closed or open), has disembarked from the plane without telling anybody of having committed the offence, and only told of committing the offence to Canadian authorities once he/she was away from the airplane, will the Tokyo Convention still apply? i.e., will the State of registration of the aircraft demand extradition of the offender to their country (in this case, Pakistan)?


text:
Why was my flight delayed and un-delayed twice?
I was on DL2941 from MSP to ABQ on June 30, which was scheduled to depart at 6:35pm CDT. At 4:48pm, I got a text saying the flight was “now departing” delayed at 8:10pm; ten minutes later at 4:58, I got another text that the flight was “now departing” at 6:35pm, i.e., on time. Then, shortly before boarding, the gate agent announced the flight was delayed, I believe to 8:05 but I’m not sure; then a few minutes later he announced that it was on time, perhaps something about “the tower”.
My question: What happened to cause not only one but in fact two delay/un-delay cycles?
According to Flightrader24, the aircraft (N3747D) had arrived from SLC that morning at 11:21am, i.e., several hours before my flight. I had looked at this schedule the day before and I’m pretty sure it was the same.
I know crew scheduling is also a thing that causes delays, but I don’t know how to obtain any public data on that. I believe weather was good at MSP, ABQ, and along the route.
I’m most interested in “teach a person to fish” type answers, i.e., how could I have figured this out myself?
This question has some good discussion of the general issues in play, but I’m interested in the specific reason(s) for my flight.

This is probably a better fit for Travel Stack Exchange.

I didn't see anything obvious after a quick glance, but one "teach to fish" source for ATC delays is the FAA's National Airspace System Status site: https://nasstatus.faa.gov
More "under the hood" information can be found at the links at the top of the page, specifically the Advisories database at https://www.fly.faa.gov/adv/advAdvisoryForm.jsp. You can also check if your flight has an Expect Departure Clearance Time at https://www.fly.faa.gov/edct/jsp/edctLookUp.jsp. Remember to use the ICAO airline identifier, not the IATA identifier (DAL vs DL).

Most non-weather delays are maintenance snags flagged by flight crews on the previous flight due to fault messages in the flight deck. These airplanes are so complex, and the components have such hard use with temperature and pressure extremes, things are breaking all the time (why there are two and three of the more important components).
The industry standard is one delay over 15 minutes, due to something in the airplane breaking or malfunctioning, in 100 departures, called Dispatch Reliability. Most mature airplanes achieve a DR between 98.5 and 99.5%. But one is a hundred is still quite a lot, and less reliable airplanes are more like 2 or 3 per 100.
The airplane comes in with a snag, and company Operations either have maintenance come to the gate to troubleshoot and fix, or unload the passengers and take the airplane somewhere to be worked on.
Maintenance will do troubleshooting and tell Operations how much time it's expected to take to fix based on standard man-hour estimates for maintenance tasks. Operations will set a new departure time.
Then the fix doesn't work, and they have to continue working on it with a new departure estimate.  Then after that, it still doesn't work, and and they either keep plugging at it, or Operations decides to switch the airplane for a spare one (some operators keep spare aircraft to keep schedule completion rates as high as possible; at this point, many operators without access to spare airplanes will simply cancel the flight).
That may not be what happened in your case, but it's a typical scenario.


text:
In a life-and-death emergency, could an airliner pull away from the gate?
Let's assume that an airliner crew has insider information about the imminent annihilation of the airport where they are currently going through boarding. They need to get away as quickly as possible. It is a regular Airbus or Boeing long-haul.
Assuming that regular airport procedures have come to a stop: At which point would they be able to leave without assistance, under their own power?
For example, normally a passenger jet is pushed back from the gate. Could it back itself out if damage to the terminal etc. didn't matter? The bridge itself is, I think, not really attached to the aircraft, so it shouldn't be a problem.
I think the ground crew usually blocks/wedges the front wheels in to ensure that the aircraft stay in its place. Could those wedges be manually removed by the crew?
Anything I miss that would require specialists or special gear on the ground before an airliner could pull away?

Could someone manually remove a chock? Yes, that's how the ground crew do it...

there's an enjoyable S.King's Langoliers vibe in this one, and a (maybe less enjoyable) Beebo Russell too

@user721108 Re Beebo Russell: Well, the crew is on board, fully professional and capable. And smart. :-).

@Peter-ReinstateMonica imo if one single dude is smart enough, one full crew can do whatever is needed by splitting tasks =)

The timing will be important.  A plane during boarding might not have the engines running and dependant on ground support, so cannot just leave.  Once the engines are started life will be easier to leave.  Engines off it will be more of KYAG.  First is kiss, last is goodbye.

It is much easier for an aircraft with tail mounted engines e.g. MD-80 or modern biz jets. In fact MD-80 was authorized for powerback from the gate

You might be interested in [worldbuilding.se] "Worldbuilding Stack Exchange is a question and answer site for writers, artists and others using science, geography and culture to construct imaginary worlds and settings."

@Jamiec Yes, thanks. I chose to ask here because the question is fairly technical and aviation-specific and (hopefully only with respect to the aviation issues) real-world based. The technical details are not so much related to the story setting.

A case where a main engine was left running during the airport stop: Air Ontario Flight 1363. Discussed in detail here https://youtu.be/a0VPBZbiAdk?si=a8pa6fqZwUT6L-aI&t=2667

Assuming that regular airport procedures have come to a stop: At which point would they be able to leave without assistance, under their own power?

Here are some ideas for a scenario where the ramp personnel is not helping for the departure.
Precompressed air and electric power
In most cases at large airports the aircraft doesn't use its internal APU (a small turbine supplying both compressed air and electric power) to save noise, pollutants and cost.
Instead there are connections to the bridge, to a truck or to the ground. For example the preconditioned air used for air-conditioning flows in these yellow flexible pipes (see @Ralph comment):

Source.
Other connections: Water, wasted water, fuel
There can also be other connections still in place (fuel, water, wasted water). The crew would need to disconnect corresponding pipes and cables; it's possible and that doesn't require any tool.
Here is a typical ramp scene for the A320; vehicles do not come or leave at the same time:

Source: Airbus, Airport and Maintenance Planning.
Everything must and can be disconnected
Everything must be disconnected without damaging the sockets. It would be hazardous to just move the plane until the connections break, e.g. the refueling nozzle would likely stay connected to the wing tank, allowing fuel to leak (see mechanism here); with engines running a fire is almost certain.
The aircraft crew can still go down the ramp using the bridge stairs (below the bridge on the first photo) and disconnect everything.
Ramp obstacles
The crew may also have to move some cart, truck or generator that might be in the way, but that should be manageable.
Open doors, servicing panels, locking devices
There are other points to be considered, like open doors and panels (on engines, on cargo holds, etc), chocks in place, gears moored with mechanical anchors. All of them are manageable without ground support. You can read about these elements on the same linked Airbus document, e.g. the connection points are all described at page 204, and mooring anchors at page 190.
Risks associated with powerback
Using reverse thrust to taxi back is possible but not entirely safe. In normal conditions such operation would have to be validated by the operator and the airport using OpSpec C065.
Taxi and take-off roll times
It can take time to reach the runway, depending on the airport layout. Taxiing faster than the allowed speed is not an option.
It also takes some time to align and accelerate for take-off.

Such departure in a novel would be credible to a pilot, providing the crew takes the related actions.

Great! Also a valuable document in the link.

If we assume the fueling & loading are complete and they're just waiting for a tug to come give them the push-back, how much of that would still be attached? I imagine they'd still be hooked up for external power & air until just about the last minute, but would anything else still be connected at that point?

@DarthPseudonym: When the push-back truck is about to make contact, the APU has been started, the only connection left is the intercom with the wingwalker or the truck driver for a towbarless truck.

"Taxiing at high speed is not an option."  Oh? I can think of a few places (airlines, and airports both) where it's fairly well S.O.P.!  That aside, great answer!

@RalphJ, I agree, that's not what I wanted to say (which was faster than usually).

Detaching comm cords & towbar would be straightforward. Getting out of a towbarless tug would be more involved, if they'd already captured the nosewheel. For storytelling purposes, if the author doesn't want to explain towbarless pushbacks, I'd suggest going with "not hooked up yet" & leave it at that.

One other thought: the air hoses are long & flexible & really, really must be secured, because an engine running at high power can absolutely generate enough suction (wind) to pull a hose right into the motor, and that is a certain way to destroy your engine. Pilots would probably be aware of this, but even in a hurry, that's not a step they can afford to omit. Maybe they could park a baggage cart where it immobilizes the hose... not normal ops, but if in 10 minutes everything is pulverized anyway... why not?

If nuclear war is really on the horizon and the pilots can convince the ground crew of the imminent danger and say "if you get the hoses, etc. removed in the next 2 minutes and climb up the stairs we'll take you with us, if not we'll leave anyway and take our chances with stuff still being connected, I think you might just get the ground crew on board (literally and figuratively).

@manassehkatz-Moving2Codidact That's a great idea, actually! I'll credit you with it if the story ever gets written :-)

In fact, I think this is very plausible if air raid sirens or the modern equivalent of warnings on everyone's cell phones have just happened and you're near a likely ground zero (e.g., you are on a plane at Reagan Washington National Airport (basically 5 miles to the White House or the US Capitol) - there are reasons for big no-fly zones and crazy takeoff and landing requirements at that airport) there is basically no way you're going to get off the plane and into anything remotely useful as a nuclear bomb shelter in 5 or 10 minutes. But use those few minutes to get off the ground

and head away from the city and you have a chance to survive. Oops. Just reread the question - this would not be "inside information", though perhaps the pilots had a little more advance notice and now everyone knows and panics...

@manassehkatz-Moving2Codidact going OT here but the idea is that civil aviation comes to a stop due to some elevated alert level (resources and airspace are allocated for military purposes) some time before an actual attack is detected and the general public is alerted.

@Peter But if it's an orderly and timed shutdown, why let people board a plane they aren't going to launch?

The only reasonable scenario I can imagine is fire on the terminal, directly at the other end of the ramp. This means get away quickly; but the airplane doesn't necessarily have to be flightworthy after, just taxi-worthy. Fuel pump will have to be shut down and fuel truck moved, but most pins can get broken.

I simply cannot imagine a scenario in which the "crew has insider information about the imminent annihilation of the airport" and in which disconnecting the bridge, fuel, water, waste and other cables, shutting all the cargo and other doors, removing the chocks, starting the engines and then using reverse thrust to back up onto the taxiway, with a high probability of striking another aircraft, ground vehicle or building, and then presumably taxi to the runway and take off without clearance, or a radio service, or having properly prepared the aircraft would in ANY WAY ever be a better option that simply leaving the aircraft and getting out of there on foot or by other means.
Never say never, but I can't imagine this would ever need to happen in any context.

Thanks for the frame challenge -- I'm trying to prepare a story where an insider has knowledge of an imminent nuclear attack on Germany, including the city they are in (probably Berlin or Frankfurt). Nothing matters except getting the airplane a few km away from ground zero, and then, preferably, on to some suddenly very attractive, poor African country that does not have any oil or other resources needed in a war. That is, damage to structures, violation of procedure, minor damage to the plane  etc. are entirely secondary. Yeah, you should avoid hitting something though, true.

Whether it's possible for the crew to essentially finish ground operation (closing the cargo door, disconnecting anything that absolutely needs to be properly disconnected etc.) are basically the details that I'd like to get some information about. Otherwise the moment of decision would have to be exactly the 5 minutes between pushback and start, which is more unlikely and more contrived.

This does not answer the question and would be better suited as a comment. "That would never happen" isn't a suitable answer to a hypothetical question.

There is a civl war. Ground personnel have already flewn. Happened before.

A similar scenario has actually happened. BA flight 149 from London to Malaysia landed in Kuwait two hours after the start of the Iraqi invasion in 1990. If the captain had been told about the invasion by BA after landing, then an emergency unauthorised departure would have been the correct thing to do. As it was, the crew and passengers were captured by Iraqi forces and used as human shields for several months. I had a friend in the cabin crew.

The crew could simply ask the ground staff (who would be there anyway) to expedite the clearance, but without authorisation, it is very improbable, meaning "crew knowledge" would be insufficient for a fast getaway. A localised event in the terminal - fire, bomb, attack etc, - would be sufficient to encourage the ground crew to expedite departure, or at the very least, separation from the terminal, making a fast departure more possible.

Yes, interaction with the ground staff is also a possible path. (There will likely be some interaction with the tower where the pilot has an acquaintance who ignores some shutdown orders by the military advance command, something along those lines.)

For example, normally a passenger jet is pushed back from the gate. Could it back itself out?

Not really, a jetliner doesn't have a reverse gear
It must be pushed back by a pushback tug. In the recent past there was the idea of electrifying the nose landing gear to get rid of the pushback tugs and to move the airplane toward the runway without using the engines to save some fuel but I don't know what happened to this idea.
You might resort to use the thrust reversals to "powerback" from the gate: it was used in the past and it's something no more usually done as explained for example here but it can be for sure used in your story.

"When reverse thrust is used to push an aircraft back from the gate, the maneuver is called a powerback"? The reason it's not done is possible damage to near-by structures, I thought.

Actually, the first google hit using the specific keywords (that didn't occur to me before)  is an aviation SE answer! ;-).

Damage to nearby structures is likely to be of lower concern, if you're convinced they are about to be annihilated, I guess.

Furthermore, not all thrust reversers are actually capable of producing reverse thrust at static conditions.  Many would actually be better called 'drag generators' than 'thrust reversers'.  Imagine the flow into the engine.  Most 'reversers' turn the flow.  If they turn the flow up to 90 degrees, the axial component of momentum is reduced (causing drag in forward flight), but not negative thrust at static conditions.  For that, they must turn the flow more than 90 degrees.

Eastern used to power back in the 80's. No tug required.

@RetiredATC AA powerbacked their MD-80s until the early 2000's. Definitely caught your attention in the terminal.


text:
How do engineers log airplane maintenance?
Is there an encoding system that replaces the vagueness of natural language when it comes to logging aircraft problems or repairs that took place at a specific site on the airplane?
So, instead of someone having to enter a description like:
"Hydraulic fluid change at system ABC"
Which would be in their own native language and filtered by their own personal level of awareness, they could enter something like:
"GF65Z ABC"
Therefore, internationally, GF65Z could correspond to exactly that type of intervention with some hydraulic system and that would also make further investigation, in the case of some problem, easier.
Anywhere I can find more information about something like this?

To go along with @ratchet freak's answer, machine parsing comes more into play when reporting maintenance status and readiness statistics, and for trend analysis - in other words, high-level aggregation and dissection of user-inputted data.  At this level, managers are more concerned with the number of aircraft available for use rather than the last time a particular aircraft's tires were kicked changed.  Typically, this is all done using pricy electronic logbook software, and would be used by large organizations with lots of equipment to track and the money to employ such a system.
Take, for example, the United States Army.  Its program of record for aviation maintenance and logistics is called Unit Level Logistics System-Aviation, or ULLS-A for short.  This software suite automates a lot of the manual forms that the Army uses.  At the most basic level, aircraft maintenance is recorded using DA Form 2408-13-1, according to DA Pam 738-751.  The time and date of each status is compiled into a daily statistic, which is then rolled up into a monthly report, often only detailing (aside from the hours that aircraft was available for mission) what subsystem was responsible for the majority of each aircraft's downtime.  Here's what a blank maintenance form looks like:

As you can see, there are a multitude of blocks, each with its own list of codes.  For instance, here is a list of the codes for WHEN DISC (when discovered), from Table 1-6 of DA Pam 738-751:
B   Handling
D   Sustainment facility (depot) level repair/overhaul/rebuild
E   Storage
G   Flight
H   Phase maintenance inspection (PMI, PPM, PMS2/3 and Reset)
J   Calibration
K   Unscheduled maintenance
L   Maintenance operational check
M   Maintenance test flight and/or functional check flight
N   AOAP results
O   Special inspection, scheduled maintenance
P   Diagnostic test (health and usage monitoring device and/or sytem)
Q   Servicing
R   Rearmament
S   Reconfiguration
T   Preflight inspection
U   Thru flight inspection
V   Post-flight inspection
W   Acceptance inspection
X   Daily/PMS/PMS1 inspection
Y   Intermediate inspection
Z   Periodic inspection

However, not all blocks are required to be filled out when using paper logbooks (believe it or not, still in use in some places); in addition to WHEN DISC, HOW REC, MAL EFF, WUC, ACTION CODE, and CAT are optional entries, and in practice never get used.  In contrast, these are required fields in ULLS-A, and so the system provides a number of helps to the user so he doesn't have to refer to the manual all the time.
Overall, only these codes (and not the free text fault/remarks block) will be machine-parsed, for the purpose of high-level analysis to determine trends and/or systemic issues affecting the entire fleet.

Thank you very much for the comprehensive response. I work in healthcare which shares similar risks in terms of loss of life with aviation and encoded information is used everywhere (e.g. http://apps.who.int/classifications/icd10/browse/2015/en). It was natural to ask myself if there was something that aviation might be doing much more efficiently. To an extent, aviation and healthcare probably involve a similar amount of surprising realisations of how things are actually managedin the field.

"Optional codes and never get used". The NAMP is like the mirror-universe version of this.

Natural language is concrete enough for this purpose, the logs aren't meant for machine parsing but instead for pilots, inspectors and other mechanics.
Having such a code system requires mechanics to memorize all of the codes or have a massive list handy when filling out the logs.
Also making such an international code system requires agencies of all countries/manufacturers to sit together and set those codes for all possible maintenance actions. There is a very high chance an action will be missed so a natural language box for "additional comments" is still required. It also needs to be rolled out to the actual mechanics filling out the logs.

While it's not possible to code every repair or maintenance action, some standard language does exist. For example annual inspections are often signed off with a stamp: I certify that this AIRCRAFT has been inspected in accordance with an ANNUAL inspection and was determined to be in an airworthy condition. -- Similarly airworthiness directives & Service Bulletins are usually logged as CW SB 2014-01-01, next due xxxx ("Complied With") or PCW AD 2014-01-01 by replacement of widget ("Permanently Complied With"), and implicitly reference the AD or SB for actions taken.

Also, a list of opaque alphanumeric codes would make data entry mistakes very common.


text:
Have any countries considered allowing supersonic flights overland?
The Concorde (partially) failed due to the lack of overland flying permissions, which in turn was due to the loud boom experienced by ground observers. But (in theory) it would be perfectly safe to allow such flights at the cost of some discomfort for local residents who would periodically hear loud booms in their neighborhood.
Have any countries (say, the Soviet Union?) considered ignoring the concerns of ground observers and allowing such flights overground, at least for certain limited routes avoiding major cities? This might be tricky in Western Europe but would otherwise be feasible in less dense parts of the world.

Related: Why was there no issue with the Tu-144 flying above land?

In the Sixtes, sonic booms were not that infrequent in Europe. NATO airplanes exercising over West Germany regularly broke the sound barrier. East European air forces trained less but took even less care of avoiding sonic booms.

I can confirm. For half of the eighties, we lived ~100 km from Ramstein and ~30 km from Frankfurt, for the other half, we lived ~75 km from both. I believe there was also a MOZ for training not far. Sonic booms were completely normal – after all, it is hard to train far away from population if the entire country is just 20 minutes "wide" for a jet fighter at top speed.

In the US, there are low and high-altitude supersonic testing corridors in southern California. People in northern LA county and southern Kern county and adjacent areas are accustomed to occasional sonic booms. Also, White Sands in New Mexico and now an area of Kansas have supersonic test airspace as well. When an airplane was hijacked in Washington, some Oregon NG Eagles boomed the Pacific northwest enroute to intercept. When the Chinese balloon was shot down, there were booms. I'm guessing the intent of the question is for purposes of regular commercial operation.

Also, when the Space Shuttle landed and when the SpaceX boosters return, there were/are significant overpressure spikes. The X-59  is preparing to test supersonically over land, including over communities not normally exposed to booms to gather data on human perceptions to a shaped and reduced boom signature.

As a side note (pun intended), it's important to point out that significant noise events can occur over land from aircraft operating supersonically over the ocean. Two examples are F-22 flight testing miles off shore in the Pacific that occasionally startled coastal residents and reports of mysterious sounds in the northeastern US possibly from the secondary carpet of the Concorde far offshore (c.f. Acoustics Today magazine, Spring 2015, volume 11, issue 2.

@mins https://boomsupersonic.com/ is trying to bring back supersonic flights, just like Elon unilaterally brought back rocket launch capability to the US.


text:
Why aren't auto-pilot systems used on helicopters to make them trivially easy to fly?
As far as my understanding of helicopters goes, it is generally much harder to learn to pilot a helicopter when compared to a plane. This is because a helicopter is naturally unstable and would crash if left on it's own, while the airplane has aerodynamic stability when up in the air.
But why aren't there auto-pilot systems for helicopters to take all the difficult work away? There are already auto hover systems available for helicopters, so shouldn't it be possible to manufacture a helicopter that is trivially easy to handle?
Obviously a lot more goes into piloting than just controlling the aircraft, but it would be great to be able to skip a large chunk of it.

Related.

This is because a helicopter is naturally unstable and would crash if left on it's own, while the airplane has aerodynamic stability when up in the air  Nope.  A "naturally unstable" helicopter won't fly. The challenge of designing an effective helicopter is to account for that which works against stability. But why aren't there auto-pilot systems for helicopters to take all the difficult work away? There are, so you are assuming an answer into your question, which is an invalid form of asking a question.

A good number of people who thought that fixed wing aircraft, and rotary wing, aircraft are "trivially easy to fly" are now dead.

Assuming rotorcraft autopilots don't exist seems contradictory with this answer: "All modern offshore helicopters that I've encountered have them and they are used extensively. Usually they are engaged shortly after take-off and disengaged shortly before landing."

You need fly by wire not auto pilot

not true entirely about stability of aircrafts. All fighters now are statically unstable and wouldn't fly without FBW. Some are so highly unstable in certain conditions that they can diverge from stable condition within fraction of seconds.


text:
Why aren't airports built with future expansion in mind?
There are currently numerous controversies around the world in regards to airport expansion, where local residents are opposed to new runways or changes in the hours of operation. The most famous example is probably Heathrow airport, where it took decades to finally approve a plan to add a third runway.
But why aren't airports built in a way where future expansion is possible? E.g. why wasn't an area 5 kilometers around Heathrow reserved for new terminals and runways, even if it wasn't clear if they're ever going to be required?

Land is expensive.

So you want to reserve a lot of land, in a heavily populated area? What happens when 5KM isn't enough? 10KM? Or what if it is way too big, and now you're just sitting on a huge tax liability? Do you sell it? The future is hard to predict.

@RonBeyer it could also be sold with an explicit condition of requiring the owner to sign a waiver promising to never protest future expansions and promptly leave their house if the land is needed.

So why not just have a law such as eminent domain and take it when you need it? The property terms you suggest would make land worthless, nobody in their right mind would buy property with that kind of vacate term. In England this is called "compulsory purchase".

@RonBeyer unfortunately politicians are reluctant to use eminent domain: https://politics.stackexchange.com/questions/23892/why-are-european-politicians-usually-reluctant-to-use-expropriation-to-speed-up

KDEN absolutely was built with the possibility of future expansion in mind.  But, it had to be built far, far away from town in order to do so.

@Ron Beyer: Because the public tends to object when you do things like that, which means that you (or your elected bosses) don't get re-elected.

Even if you found someone willing to take the deal, no half-sensible lender will write mortgages against property where there's an agreement to vacate at any time if the land is needed. You might be interested in avigation easements though, which permit overflights, prevent property owners near the airport from building tall structures that would interfere with airport operations, require airport-compatible land uses, and usually have some kind of agreement not to sue the airport over noise, perhaps offered in exchange for cash and/or noise-proofing services.

Many European airports are built relatively close to the cities they serve. Airports in the US are (in general) further away, where an expansion is easier to do, e.g. Denver International Airport:

The distant location was chosen to avoid aircraft noise affecting developed areas, to accommodate a generous runway layout that would not be compromised by blizzards, and to allow for future expansion.

Heathrow on the other hand is old. It has such a long history that it has its own Wikipedia article (which ironically starts in 1410!). It started as a small airfield in the 1930s and it was in a very rural area at the time:

The land was at the time used for market gardening and wheat growing.

It was then greatly expanded as a military airport during World War II. After the war, the airport was turned into a civilian airport. The original runway layout way quite different compared to today, as the following image from the 1950s shows:

(image source: Wikimedia)
This image still shows the rural surroundings. But London expanded further and further and eventually the airport was fully surrounded:

(Google Maps)
Why was the land not reserved?
Because land in London is extremely valuable. The time after World War II saw the greatest expansion of London (size wise, not population wise):

The population peaked in 1940 at around 8.5 million, before declining and then rising recently to just over 8 million. Despite the decline and the devastation caused by the second world war, the 20th century saw the largest urban expansion in London’s history.

(The Guardian)
At the same time, other airports were expanded to serve the Greater London area: Gatwick was expanded during the 1950s, Luton in the 1960s and Stansted was converted to a civilian airport in 1966. With all of these airports available, there was no need to anticipate a large expansion of Heathrow. The land was much more valuable as an urban area.


text:
When can a tower's callsign differ from the airfield name, and how do I find the proper callsign?
It seems like a lot of air traffic control towers use callsigns that are much different from the name of the airfield.  For example, Lehigh Valley International (ABE) has "Allentown Tower."

"Allentown Tower" doesn't appear anywhere I can see on the sectional chart.  (The control frequencies tab even lists it as "Lehigh Valley Intl.")  You might be able to figure it out through other hints, such as the presence of the "Allentown Class C," but that doesn't seem like something that can be relied upon in general.
I doubt pilots are expected to have airport diagrams handy for every airfield in the vicinity just for this.
If, say, I had to divert to an unfamiliar airfield, how would I find the proper callsign for its tower?

I doubt pilots are expected to have airport diagrams handy for every airfield in the vicinity just for this.

And you're wrong to doubt that.

If, say, I had to divert to an unfamiliar airfield, how would I find the proper callsign for its tower?

From the chart. Same place you'd get the tower frequency...

By "chart," do you mean the airport diagram?  (As opposed to the sectional chart, which is where I would get the tower frequency.)

@Maxpm The sectional. It has a magenta box that says, "contact Allentown app" with the correct frequencies.

@TomMcW Unfortunately, I don't think that's a reliable method, in general.  Perhaps a better example would have been the nearby Essex County Airport (CDW), which has "Caldwell Tower."  There's nothing on the chart referring to any "Caldwell."

@Maxpm Hmm. On paper charts it would be on the back. The definitive source would be the chart supplement, but that's pretty impractical in flight. You could tune the freq and listen for it. But I'm sure if you said the airport name it wouldn't be the first time the atc has heard that.

What do you do in places where there are too many nearby airports to carry charts for all of them?

@Vikki carry more charts... Pilot bags are large enough to hold them all for a very wide area, they don't take up too much space. Several hundred of them take up about the same space as a paperback novel, that fits anywhere


text:
What is a navigational fix? Where can I get navigational fixes for a local airport?
Amateur in aviation, so please explain the purpose of navigational fix and its characteristics. How is a navigational fix being placed around the runway, or how it is determined this would be the right spot? How does it help a aircraft to make it land?
And where would I get the details of navigational fixes for a airport near me? Is there a API, does ICAO provide any info?
Any links/charts could be of great help.

We may not be able to get this answer to you before you run out of fuel.

In general terminology a fix is the result of a process you perform to find out your own current position. The position of an airport (it's location) or some other place (e.g. a navigational waypoint along a planned route) is it's coordinates not it's fix.

A navigational fix is a waypoint that can be used to navigate to, from or between airports or other navigational fixes. Navigational fixes can be GPS-based coordinates, radio-based navigational aids like VORs or NDBs or airport themselves, which have a defined airport reference point with set coordinates.
Navigational fixes or aids are usually not placed around runways, but those that are used for approaches or departures (mostly VOR or NDBs) are placed at or in the vicinity of the airport. See below for the placement of the Barmen (BAM) VOR, which is one of the approaches fixes used for the ILS approach to runway 23L and 23R and the, nowadays no longer used, NDBs DX and LI as the outer markers for the instrument approach.

(Image Source: www.skyvector.com)
Navigational fixes required for approaches or departures to a specific airport will be available in the countries' AIP, in the publications for the specific approach or departure routing, e.g. navigational fixes along a STAR or Transition from the Initial Approach Fix (which is a navigational fix as well) to the Final Approach Fix.

(Image Source: VATUSA)
The above displays the navigational fixes for the transitions/arrivals into Memphis International Airport.
For a list of available radio navigational aids around an airport, you can try sources like SkyVector.

This is a very broad question, but I'll give it a shot:
Why do Airplanes need navigation?
Navigating an airplane is like driving a car with sole reliance on maps. Except you don't have any signs hanging in the air that might give you hints where to go, and in bad weather it is hard to determine your position by looking down to the ground. Thus a pilot needs other means of position determination.
Flying goes back over 100 years now; way before people even thought about GPS being possible, flights were already made by reference to navigation aids. A (by now) kind of old fashioned navigation aid is the NDB(Non-Directional Beacon) which in its day's was very helpful and was even used for approaches! This is now replaced by VORs (Very high frequency Omnidirectional Beacons). Building a VOR is quite a task, in the US there are many compared to other countries, yet not enough for the amount of traffic.
Why are there Navigational Fixes?
Cars use streets to get from A to B. Imagine all air traffic going straight from their departure to their destination airport, this would end in a huge chaos. Therefore there were "streets", so called airways, established from  one VOR to the other. Traffic flies along these routes, just like cars drive along streets. But the VORs only are still not enough points on the map to navigate traffic. A simple curve would need multiple VORs to be described (Yes, there are arcs around VORs but that's something different). Thus waypoints were created. Before the time of GPS they could usually be identified by two radials from two different VORs. By now there are more waypoints out there that are described by coordinates only and can only be used with a GPS.
Where are navigational fixes placed?
Usually they are placed in a way so that they help out in coordinating traffic. You will most likely find more fixes around airports, as they offer possibilities to controllers to spread the traffic and, whats even more important, guide planes to the runway. There are so called STARs (Standard Terminal Arrival Route) which bundle traffic approaching the airport from different directions towards the same runways, followed by transitions which guide them via the IAF(Initial Approach Fix) to the final approach. All those procedures are described using the waypoints, VORs and other navigational aids.
Where would you get details about fixes?
To be honest, I don't know of any source that can be used for real world flying. I know of databases used for simulator flying, which are still up to date and probably contain almost exactly the same information. Those are called "AIRAC" (not to confuse with the real world AIRAC cycle though!) and can be downloaded or come with certain programs. From there you should be able to get the information you need (if you want to write a program using this information). Again, these are not for real world flying! If you are just curious about the waypoints around you, this website is one example of a source for these kind of things (clicking "World Lo"/"World Hi" will display these waypoints).
I hope this answers your questions, if not try to ask a bit more precise!

Hehe... beat you by 30min! :D Nice answer, though!

For real flying you get appropriate navigational charts and they have the points marked on them with appropriate definitions. And if you have a flight management system, there will be database for it that again has all the points and airways. For real flying, nothing tends to be free or course.

Agreed! But of course those charts can not be used as an API or similar.


text:
What is the methodology for assigning airport codes?
Pearson airport in Toronto has the airport code YYZ, which does not reflect the name Pearson or the city of Toronto. This seems contradictory to other IATA codes like LGA (Laguardia), JFK (John F Kennedy), LHR (London Heathrow), and DFW (Dallas Fort Worth).
Is there a specific methodology in place for assigning these values?

Possible duplicate of http://travel.stackexchange.com/questions/7236/whats-with-canadas-airport-codes

There are different kinds of codes assigned to airports. IATA codes, which are the three letter codes you mention; are for travel industry identification purposes (by the way, these aren't restricted to airports - train stations also have these codes). These are used by airlines and travel agents.
The other four letter codes are ICAO codes. These are used for navigation, air traffic and flight planning.
ICAO codes have a defined standard, each region is assigned a letter and all codes begin with that letter. Canada is assigned a practical C, US is K:

IATA codes however, are arbitrary. For some reason, Canada was given 'Y' and so all IATA codes in Canada begin with Y.
There is YYC (Calgary), YVR (Vancouver), but then you have YQX (Gander) and YXS (Prince George) and YUL (Montreal-Trudeu).

I have heard a rumor that the "Y" in Canada is an indication meaning "Yes there is a weather station at this airport" (or at least it was originally). IATA codes are used by the airlines so it makes sense that they would only go to airports with weather reporting capability, but not all airports in Canada follow this pattern, for example CSD4 (which does seem to have WX reporting) and CMB7 among others.

Airport codes in the US and Canada were originally based on the two-letter weather station codes for nearby cities. For instance, Toronto (Pemberton) was "TO".
However, it was soon apparent that didn't provide enough codes, so it was expanded to 3 letters. Canada chose to prefix all their codes with "Y" so they would be easily recognised, e.g. "YTO" for Toronto, whereas the US added a suffix letter, such as "LAX" for Los Angeles. These are the IATA codes you know today.
Then ICAO wanted even more codes to cover the entire world, but assigned on a more geographical basis than the seemingly random IATA codes. Canada was prefixed again, this time as region "C", e.g. "CYTO", and the contiguous US was prefixed as region "K", e.g. "KLAX".
When Toronto Pearson airport was built, it needed a new code because YTO/CYTO was already taken; I can only guess that they chose YYZ/CYYZ because there was no weather station using code YZ. Canada later added Z/CZ prefixes, and now allows any letters just like the US.
Note that the US and Canada got single-letter ICAO prefixes due to their large land area. Most countries are smaller and thus got two-letter prefixes, with the first letter specifying a region, e.g. "E" for Northern Europe, and the second specifying a country, e.g. "G" for Great Britain. This leaves no obvious mapping to/from the IATA code, e.g. EGLL vs LHR.

The "K" prefix only applies to the 48 continental US states.  Hawaii and Alaska are part of the Pacific region and thus use the prefixes "PH" for Hawaii and "PA" for Alaska.

@Gerry Fixed that.

There's a missing step in this explanation of where IATA codes came from: the "I" in both IATA and ICAO stands for "International", so both sets of codes "cover the entire world". IATA's coding directory does not include every weather station, and the FAA's does not include non-US airports. They even use conflicting codes sometimes: "BER" is the IATA code for the new Berlin Brandenburg Airport; but also the FAA code for Adak Island, AK.


text:
What determines in which direction a runway is used?
A nearby airport has a single 05/23 runway (3900m long), where airplanes start and land in one direction during certain periods and in the opposite direction during other periods.
How is the direction determined -- I assume it's air traffic control which decides that but based on what ? (wind, sun ?)

Wind direction mostly, planes take off best when facing in the wind as that means free airspeed so the takeoff roll is shorter.
In busier airspace (with multiple towered airports) each airport coordinates the corridors so they don't intersect depending on available runways, prevailing winds and relative demands on the airports.
It is possible that it is dictated by noise abatement measures so night time flights pass over a nearby forest rather than wake up the capital.

or the other way around. What with environmental regs ever more putting small furry creatures above and ahead of humans...

Early airfields had a number of intersecting runways so that the one most closely aligned with wind direction could be designated the active runway. An example is London Heathrow which briefly had six runways intersecting in a star of David pattern. Nowadays aircraft are better able to cope with cross-wind landings, but it is still advantageous to take-off and land into the wind.

There are several factors:

Prevailing winds
Neighboring airport traffic patterns
Size of inbound aircraft
Where the aircraft is coming from
Final parking space
Congestion
Fuel status
Weather (thunderstorms)
Noise considerations

At small airports, it is usually just the runway that faces into the wind and can accommodate most of the traffic coming in.
At large airports, the wind dictates which flow is being used (like a "north flow" or "south flow"). From there, aircraft usually are assigned to land on which ever side of the airport their arrival procedure brings them to. Sometimes, it is also decided by which gate/terminal they'll be parking at. Lastly, the available approach procedures can change things if the weather is not good

At some small mountain airports, it's not physically possible to use both ends of the runway - airplanes must land one way, and take off in the other direction, due to nearby mountains.

@fluffysheap: And some airports have the same sort of restriction for other reasons; for instance, runway 14/32 at Logan.

Runway in use is based on wind, most of the time, with aircraft taking off into the wind. In some cases, when the wind is calm, airports have a default runway (it usually has better lighting, or approach systems for aircraft to use during conditions with poor visibility).

Most aircraft have a max tailwind limitation (those I've flown had a limit of 10 knots).  So for convenience, a pilot could take off with up to that 10 know tailwind, but not with a stronger tailwind.  Depending on runway length, and aircraft gross weight, it might not be possible to takeoff with the full max tailwind, necessitating a takeoff into the wind anyway.
Some runways are backed up against hills or mountains, and aren't safe to takeoff in that direction, so always land toward and takeoff away from the rising terrain.


text:
Do F-22 and F-35 use force sensing flight sticks like F-16?
Do F-22 and F-35 use force sensing flight sticks (as opposed to flight sticks that actually deflect and sense movement), like F-16?

They move, pretty much like an F-16 stick.
From this MIT lecture "F-22 Flight Controls", Lt Col Randy Gordon, F-22 test pilot (from the transcript):

It's a side stick.
Initially it didn't move.
Eventually they decided, I'll put in some deflection.
So I can go a half inch left, a half inch right, about a quarter inch
forward, I go about a half inch back because normally I really want to
get the nose going this way.
There's some deflection to give you feedback that you've input
something on the stick, but not so much deflection that it gets in the
way of everything else you're trying to do.

Thank you for that edit. I was just about to do that.

AFAIK, the "didn't move" lesson was learned on early F-16. The F-22 stick was movable (but force-sensing) from the beginning.

Yes. And I believe that is what he is referring to in the presentation. Of course, we'd have to ask him for specifics.

The F-16 always moved; Deflection was increased when it went into production. The F-22 deflection is about 10 times the F-16. The F-35 is an active stick and can be programmed for resistance and travel.

Sources for this info?

I played with flight control stick in pre-production F-16 at Eglin AFB in 1980-1981, and as I recall, it did not move. I was told that it was an issue and that they were modifying it to move a small amount to provide feedback to pilot.

I worked with the General Dynamics engineer that designed it. I saw it disassembled. I saw the transducers that measure displacement. No strain gages.

I defer to your recollection. My comment was based on 50 year old memories and 15-20 minute conversation with AFSC test pilot. Also, there was no power on the jet when I sat in it and played wuth the flight control stick.  One clear [related] memory was the Ace bandage he wore on his forearm, that he said helped prevent blood spots on his skin. Not sure if he was pulling my leg, (arm) with that one.

It’s a persistent myth. He was adamant about it and showed me the detail drawings and the Acceptance Test Procedures that measured the deflection. It’s a passive stick controller with a coil spring to provide the “feel” resistance.


text:
What is this guy doing while walking along with the moving plane at the FRA airport?
While the aircraft was moving backwards (targeting takeoff), a guy was attached to it by a thread, probably "listening" to something, and was following the plane by walking at the same pace.
That was at the FRA airport.
What is this guy doing exactly? Does this job have a name?

"Fourth class ticket."

"Taking the plane for a walk."

That's the power cord for the engines.  It's really, really long.

that's simply a long headphone cable (exactly like your headphones, casques, at home) - to talk to the pilot